Thermo-mechanical properties of nano-scale freestanding aluminum films

Nano-structured thin films are shown to possess superior mechanical properties when compared to their bulk counterpart. However, reduction of length scale also makes them sensitive to thermal field. Elevated temperatures due to heat dissipation may change the mechanical properties and hence affect the reliability of nano-scale thin films in micro/nano-scale devices. Thermo-mechanical properties of thin films are typically studied on substrates, which makes isolation of the substrate effect difficult. To avoid this problem, we have performed temperature controlled tensile experiments on freestanding 150 nm thick (average grain size 65 nm) aluminum films using micro-electromechanical systems based testing platform. Experimental results for temperatures from 17 °C to 162 °C show expected decreases on yield and ultimate strengths and increase in ductility. An unexpected pronounced reduction in the Young's modulus and strength at or above 75 °C (bulk aluminum starts to show such behavior only at or above 200 °C) was also observed, which could be due to combined effect of length-scale and time dependence of anelastic relaxation in the material.